1. Field of the Invention
The present invention relates to a light source device, more particularly to a light source device having a high pulse rate and capable of emitting a high-luminance radiation pulse.
2. Description of the Related Art
In an exposure apparatus for use in manufacturing an LSI, far-ultraviolet light has been widely used as exposure light in order to further enhance resolution. As a light source for generating the far-ultraviolet light, a pulse-driven excimer laser has been widely used. Meanwhile, it has become an important subject to enhance a pulse rate of an exposure light source in order to enhance a processing speed during exposure and to improve throughput. Particularly, in an exposure device of a scan system, which uses a pulse light source, it is strongly demanded that the pulse rate of the light source be further enhanced from a viewpoint of improving the throughput. Meanwhile, since the pulse rate of the excimer laser is no more than about 200 Hz, it is strongly demanded that the pulse rate thereof be enhanced. As a method of enhancing a pulse rate, for example, an attempt to enhance a gas flow rate in a tube of the excimer laser has been made.
Moreover, in a microscope or an optical inspection apparatus, since luminance of an illumination light source is sometimes short in the case of executing high-speed observation or high-speed inspection, development of a high-luminance light source as an illumination light source is demanded.
As a method of enhancing a pulse rate of an excimer laser, a method has been proposed, in which a gas flow rate in a tube is enhanced. However, enhancement of the pulse rate has limitations only by improvement of the gas flow rate, and actually, the pulse rate cannot be enhanced to a desired pulse rate. In addition, when the gas flow rate is wished to be enhanced, a structure of a laser device is made complicated, and a manufacturing cost thereof becomes expensive to a great extent.
Moreover, as a method of enhancing luminance of a light source such as a lamp, conceived is a method of increasing input power. However, even if the input power is increased, actually, only a size of a light emission arc of the light source becomes large, and such an increase does not contribute to the improvement of the luminance very much. Furthermore, conceived is a method of enhancing a light emission rate of the light source. However, though the time-average luminance is enhanced when the light emission rate is enhanced, the time-average input power is limited; therefore, the maximum light emission rate is limited in many cases.
Accordingly, an object of the present invention is to provide a light source device capable of further enhancing an effective pulse rate.
Another object of the present invention is to provide a light source device capable of generating a high-luminance light pulse.
A light source device according to the present invention comprises: a plurality of light sources emitting light; a rotating reflection body having one or more reflection surfaces and emitting the light emitted from each light source along an optical path common to the light source; a position detecting device detecting a position of the reflection surface of the rotating reflection body; a timing control circuit generating a synchronization signal for driving the plurality of light sources in synchronization with the position of the rotating reflection body based on an output signal from the position detecting device; and a power supply circuit sequentially pulse-driving the light sources based on an output signal from the timing control circuit.
A basic concept of the present invention is based on recognition that a plurality of light sources disposed at spatially different positions and emitting light while being displaced with time are synchronized spatially with time, resulting equivalently in that the plurality of light sources exist at spatially the same position. Based on such recognition, in the present invention, used is the rotating reflection body emitting light made incident from various directions along the same optical path in order to spatially synchronize the plurality of light sources disposed at the different positions. Moreover, in order to synchronize the light sources with time, used is the position detecting device detecting positions of the reflection surfaces of the rotating reflection body. And, based on position information from this position detecting device, a synchronization signal synchronized with time is generated. Then, a pulse-shaped drive signal is generated from the power source for driving the light source based on this synchronization signal to sequentially drive each light source. Consequently, a plurality of pulse light sequentially emitted from the plurality of light sources can be sequentially emitted along a common optical path, and the pulse rate is multiplied by a multiple of the number of the provided light sources. Thus, it is made possible to increase the effective pulse rate as a light source device. Simultaneously, accompanied with the increase of the light emission rate of the light source device, the time-average luminance is also increased; consequently, an effective luminance is also increased as a light source device for illumination.
Note that, in this specification, the term xe2x80x9clightxe2x80x9d includes electromagnetic waves having a variety of wavelength bands such as infrared light, visible light, ultraviolet light and an X-ray. Emission of the ultraviolet light includes electromagnetic radiation of the entire ultraviolet bands of DUV, VUV and EUV. Moreover, the term xe2x80x9clight sourcexe2x80x9d means light sources generating the electromagnetic waves having a variety of wavelength bands such as infrared light, visible light, ultraviolet light and an X-ray.
As a light source for use in the present invention, any light source capable of emitting the pulse light can be used, and various light sources such as a xenon flash lamp, an excimer laser and a solid laser such as YAG can be used. Particularly, the xenon flash lamp can generate high-density plasma and emit far-ultraviolet light having a wavelength of about 13 nm; therefore, the xenon flash lamp is extremely suitable as a light source for an exposure apparatus for which a much higher resolution power is required.
Note that, the plurality of light sources may be light sources emitting light entirely having the same wavelength, alternatively may be light sources emitting light having different wavelengths. For example, the plurality of light sources may include light sources emitting the ultraviolet light and light sources emitting the infrared light. In this case, the wavelengths can be selected by switching the synchronization of the rotating reflection body. For example, in response to the purpose of a target to be processed, only the ultraviolet light or the infrared light can be continuously emitted, alternatively, the ultraviolet light and the infrared light can be alternately emitted.
Moreover, as a rotating reflection body, a monogon mirror having one reflection surface or a polygon mirror having a plurality of reflection surfaces can be used. Moreover, as such a reflection surface of the rotating reflection body, a reflection surface having an aluminum layer or a silver layer coated thereon, a reflection surface having a dielectric multi-layered film formed thereon and the like can be used. And, the reflection surface can be properly selected in response to the emission wavelength band to be used. Furthermore, it is also possible to impart wavelength selectivity to the reflection surface of the rotating reflection body, and thus it is also possible to reflect or transmit only radiation light of a specified wavelength band. Hence, it is also possible to emit light of a specified wavelength in one direction and to emit light of another wavelength in another direction by combining the light with the wavelength band of a light source to be used.
A preferred embodiment of the light source device according to the present invention is characterized in that a plurality of light sources are disposed in an approximately equal interval in a circle ring shape on one plane, a rotating reflection body is disposed at a center of the circle ring, and an optical path common to the light sources is set as an axis passing through the center of the circle ring and made perpendicular to the plane. With such a constitution, a small-sized light source device can be realized, which is capable of disposing a large number of light sources adjacent to each other, utilizing the space effectively, and emitting radiation light having a high pulse rate.
Another preferred embodiment of the light source device of the present invention comprises: an excitation light source emitting excitation light; a plurality of target materials converting incident excitation light into radiation light of a wavelength different from the wavelength of the excitation light; a rotating reflection body having one or more reflection surfaces, making the excitation light emitted from the excitation light source incident onto the target materials, and emitting the light emitted from each target material along an optical path common to the target materials; a position detecting device detecting a position of the reflection surface of this rotating reflection body; a timing control circuit generating a synchronization signal for driving the excitation light source in synchronization with the position of each target based on an output signal from the position detecting device; and a power supply circuit pulse-driving the excitation light source based on an output signal from the timing control circuit. This embodiment is suitable for converting the wavelength of the infrared light into the wavelength of the ultraviolet light band such as VUV and EUV and for emitting such ultraviolet band at a high pulse rate. In this case, as an excitation light source, for example, an Nd-added YAG laser or an excimer laser can be used. Moreover, as a target, a variety of wavelength conversion materials such as tin, tantalum and gas jet of xenon can be used. Furthermore, as a reflection surface of the rotating reflection body, for example, in the case of emitting the ultraviolet light of EUV, a dielectric multi-layered film made of molybdenum and silicon can be used. Note that, when the excitation light is incident onto the target and the wavelength conversion is carried out, a scattering molecule such as a high-speed molecule and a molecule cluster is possibly generated. In this case, if the rotating reflection body is constituted of a monogon mirror having one reflection surface, since a drift speed of debris and the like is far slower than that of the light, the scattering molecule such as a high-speed molecule is adhered onto a side or a back of the rotating reflection body other than the reflection surface even if it is generated. Therefore, a possibility of contaminating the reflection surface can be significantly lowered.